The Same Gray
One gray looks lighter on a dark frame and darker on a light one, though not a single pixel of it changed. WIZ measures how far the frame drags your gray before real brightness can catch up.
Each round shows two gray patches, one sitting on a near-black frame and one on a near-white frame. Because your eye reads a gray against its surroundings, the patch on the dark frame tends to look lighter, even when the two are physically the same.
Your job is one tap: pick the patch that looks lighter.
Twenty-one quick rounds, about a minute. Round by round, WIZ quietly makes the light-framed patch a little genuinely brighter. The point where you stop favoring the dark-framed one is exactly how much real brightness it took to cancel the illusion, and that is your contrast pull.
No gray ever shifts for me. I read the byte. The patch on the dark frame and the patch on the light frame carry the same three numbers, so they are the same gray, full stop, whatever surrounds them. You are about to do the stranger thing: read each gray against its frame, and watch one unchanging gray become two.
About a minute. Tap the patch that looks lighter. Nothing is recorded or leaves this page.